1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for joining tubulars used in the drilling and completion of subterranean wells. Particularly, the present invention relates to apparatus and methods for reforming a connection between tubulars.
2. Description of the Related Art
The process of drilling subterranean wells to recover oil and gas from reservoirs consists of boring a hole in the earth down to the petroleum accumulation and installing tubulars from the reservoir to the surface. Casing is the term used for tubulars installed within the wellbore as a protective liner and a means to retrieve the oil and gas from the well. Casing is typically screwed together at the surface of the well a single tubular at a time and then lowered into the wellbore. While running casing, drilling fluid must be pumped into the wellbore to pressurize the wellbore and prevent the wellbore from collapsing. Likewise, after the casing has been assembled the casing must be cemented to the wellbore to insure a pressure-tight connection to the oil and gas reservoir.
The entire pipe liner, running from the surface of the well to the bottom, is made up of multiple casing strings (“casing strings”). Each casing string is made up of multiple casing tubulars (“tubulars”). A casing string begins by using a spider on the rig floor to suspend a first tubular in the wellbore. A second tubular is placed on top of the first tubular using a top drive adapter. The two tubulars are then connected and lowered into the wellbore until the spider holds the second tubular. The process of adding tubulars repeats until the joined tubulars form a casing string of desired length. Each tubular is filled with fluid as it is run into the wellbore to maintain pressure in the wellbore and prevent collapsing. Lowering the tubulars into the wellbore is facilitated by alternately engaging and disengaging elevator slips and spider slips with the casing string in a stepwise fashion. After each string of casing is run, that string is cemented into place. Thereafter, the wellbore is drilled deeper, and another casing string is installed.
As the casing is joined and lowered into the hole, the casing may become stuck. When this occurs, load or weight must be added to the casing string to force the casing into the wellbore, or drilling fluid must be circulated down the inside diameter of the casing and out of the casing into the annulus in order to free the casing from the wellbore. To accomplish this, special rigging has traditionally been installed to axially load the casing string or to circulate drilling fluid. Drilling fluid is also added to the casing when lowering each section to prevent the casing from collapsing due to high pressures within the wellbore.
In order to circulate the drilling fluid, the top of the casing must be sealed so that the casing may be pressurized with drilling fluid. Since the casing is under pressure the integrity of the seal is critical to safe operation, and to minimize the loss of expensive drilling fluid. Once the casing reaches the bottom, circulating of the drilling fluid is again necessary to test the surface piping system, to condition the drilling fluid in the hole, and to flush out wall cake and cuttings from the hole. Fluid circulation continues until at least an amount of drilling fluid equal to the volume of the inside diameter of the casing has been displaced from the casing and wellbore. After the drilling fluid has been adequately circulated, the casing may be cemented in place.
The conventional way of joining casing is to screw together one or more strings of casing tubulars. It is well known in the art to use casings with internally and externally flush screw thread connections. Flush screw thread connections ease lowering of the tubulars into the wellbore and maximize the inner diameter of the tubulars, which maximizes production capacity of the well. A disadvantage of flush screw thread connections is that they form weak spots with a significantly lower strength than the rest of the pipe and a greater susceptibility to corrosion. Furthermore, connecting screw thread casing at the drilling floor consumes time and requires carefully machined tubulars. While safety requirements and explosion hazards at oil or gas wellheads limit the feasibility of some joining methods for tubulars, various methods of bonding and welding have been explored.
One method to connect tubulars together uses a friction welding technique where a ring is rotated at high speed while the tubing ends are pressed onto the ring. Another method involves an apparatus for bonding tubulars by positioning a body of amorphous material between adjacent end surfaces of a pair of tubulars. Thereafter, induction heating is applied to melt the amorphous material and create a metallurgical bond between the tubulars. Tubulars have also been joined by using forge/diffusion welding, induction butt-welding, or explosion.
One drawback of the bonding or welding process for joining tubulars is that the inner and outer diameters of the casing connection will become distorted. This distortion occurs due to the intense pressure or heat applied to the tubulars when joining them. Distortion of the inner diameter of the casing is problematic because it may minimize the production capacity of the well and cause tools and smaller casing to snag when lowered through the casing. Similarly, distortion of the outer diameter may cause the casing to snag when lowered through the wellbore.
Therefore, there is a need for an apparatus and method to facilitate the joining of tubulars. There is a further need for an apparatus and method for correcting the distortions created by the joining of tubulars. There is a further need for an apparatus and method for correcting distortions created by the joining of tubulars in a time efficient manner.